Due to the increasing popularity of mobile devices and the growing development of wireless networks, nowadays automobiles are able to communicate among them and with the infrastructure using different wireless technologies, thus improving not only communications but also safety on the roads. In order to improve communications by maintaining the Quality of Service (QoS) required by applications (e.g. throughput, latency) while the car is moving, switching from one base station to another, Vertical Handover techniques are the most adequate solution. In this work we present a Vertical Handover Decision Algorithm powered by the IEEE 802.21 protocol which takes advantage of the current devices deployed in the vehicle's on-board unit by considering geolocation, car navigation and realistic propagation model of different underlying networks such as Wi-Fi, WiMAX, and UMTS. Results demonstrate that QoS can be guaranteed when location and networking parameters (such as packet delay and bandwidth offered) are jointly considered.